1. Field of the Invention
Embodiments of the invention relate to a liquid crystal display device, and more particularly to an external electrode fluorescent lamp and a backlight unit of a liquid crystal display device using the same. Although embodiments of the invention are suitable for a wide scope of applications, it is particularly suitable for improving light efficiency and reducing power consumption of an external electrode fluorescent lamp.
2. Description of the Related Art
In general, the applications for a liquid crystal display (LCD) device are broadening due to its characteristics of lightweight, thin profile, and low power consumption. For example, the liquid crystal display device is now used in office automation equipment and audio/video equipment. The liquid crystal display device controls light transmission in accordance with signals applied through a plurality of control switches, which are arranged in a matrix shape, to thereby display a desired picture on a screen. The liquid crystal display device is not a self luminous display device. A separate light device, such as a backlight, provides the light to the liquid crystal display device.
The backlight is classified as either a direct type or an edge type depending on the location of a light source relative to the liquid crystal display panel. The edge type backlight has a light source installed along an edge of a liquid crystal display device, and irradiates light onto a liquid crystal display panel through a light guide panel and a plurality of optical sheets. The direct type backlight has a plurality of light sources disposed directly under the liquid crystal display device, and irradiates light onto the liquid crystal display panel through a diffusion plate and a plurality of optical sheets.
The direct type backlight has higher brightness, more consistent light uniformity and higher color purity are higher than the edge type backlight. Thus, the direct type backlight is more often used in display devices, such as an LCD television. However, an edge type is used where a thin profile is desired, such as a laptop computer display.
FIG. 1 is a diagram representing a cold cathode fluorescent lamp of the related art. Cold cathode fluorescent lamps (CCFL) have been typically the fluorescent lamps used as light sources in the direct type backlight unit. As shown in FIG. 1, the cold cathode fluorescent lamp CCFL includes a glass tube 6, internal electrodes 2 inside of both ends of the glass tube 6, lead electrodes 4 that are in contact with the internal electrodes 2 and extend to the outside of the ends of the glass tube 6, and a fluorescent material 10 on the internal surface of the glass tube 6 at a central portion of the glass tube 6 for radiating visual light. An inner space 9 of the glass tube 6 is filled with mercury (Hg) and a discharge gas made of argon (Ar) and neon (Ne). The cold cathode fluorescent lamp CCFL uses internal electrodes that are connected to an outside wire assembly, which provides the electrical energy to generate light emission.
FIG. 2 is a diagram representing an external electrode fluorescent lamp of the related art. Instead of internal electrodes, the external electrode fluorescent lamp uses external electrodes on the external surface at both ends of the glass tube, as shown in FIG. 2. The external electrode fluorescent lamp (EEFL) 2 includes a glass tube 16, external electrodes 12 are formed on the external surface of the glass tube 16 at both ends of the glass tube 16, and a fluorescent material 20 is formed on the internal surface of the glass tube 16 at a central portion of the glass tube 16 for radiating visual light. An inner space 19 of the glass tube 16 is filled with mercury (Hg) and a discharge gas made of argon (Ar) and neon (Ne).
In the external electrode fluorescent lamp EEFL, the mercury (Hg) and the discharge gas are injected into the glass tube 16 and then the external electrodes 12 are disposed on the external surface of the glass tube 16 at both ends of the glass tube 16. If a voltage is applied between the external electrodes 12, a discharge of ultraviolet light is generated that causes the fluorescent material 20 to emit visible light. Aluminum tape (AL tape) or aluminum paste (AL paste) can be used as an external electrode 12 material of the external electrode fluorescent lamp EEFL. The internal pressure of the argon (Ar) and neon (Ne) within the glass tube 16 is not less than 50 torr and argon (Ar) is about 10% of the argon (Ar) and neon (Ne) discharge gas. However, a high voltage for discharge is required because the pressure within the tube in the related art external electrode fluorescent lamp EEFL is at a high pressure of not less than 50 torr. Thus, power consumption is increased and lighting efficiency is reduced.